Art of cracking hydrocarbons



Feb. 11, 1936. H. L. PELZER ART OF CRACKING HYDRQCARBONS Filed Aug. 28, 1931 SEE INVENTOR flarr L. Pe/zer L9 WM @Zm' W KTTQRKIEYS Patented Feb. 11, 1936 UNITED STTES ART OF CRACKING HYDROCARBONS Harry L. Pelzer, Houston, Tex, assignor to Sinclair Refining Company, New York, N. Y.. a

corporation of Maine Application August 28, 1931, Serial No. 559,870

4 Claims.

This invention relates to improvements in the manufacture of gasoline by cracking higher boiling hydrocarbon oils, such as crude petroleum and reduced crude petroleum, other high boiling hy- 5 drocarbon oils including tar constituents, gas oil, including particularly heavy gas oil, and the like.

The invention is of special value and application in the manufacture of motor fuel gasoline of high anti-knock quality from stocks containing tar constituents, so-called dirty stocks. The production of motor fuel gasoline of high antiknock quality by subjecting higher boiling hydrocarbon oils to severe cracking conditions has 1 been practiced hitherto. Such practice has, however, usually required a supply of charging stock free from tar constituents, so-called clean stock. In so-called vapor phase cracking operations, for example, distillate stocks substan- 29 tially free from tar constituents are usually required for successful operation. The production of a clean charging stock from a dirty charging stock within such on operation, as described for example in my application Serial Number 198,621

25 filed June 13, 1927, usually involves the production of an intermediate high boiling fraction. refractory with respect to the cracking conditions maintained, even though they be severe, which fraction must be discharged from the operation to maintain high production rates and high efficiency. Such intermediate refractory stocks represent a further source of motor fuel gasoline of high anti-knock quality. Also, these stocks are usually available at relatively high tempera- 35 tures as produced within the operation. The combined operation of this invention provides an advantageous method of recovering high yields of motor fuel gasoline of high anti-knock quality from charging stocks containing tar constituents.

40 As will appear, however, the invention is, in some aspects, of broader application.

The complete combined operation of the present invention comprises three general steps; the second step is advantageously included in the .15 combined operation but, in one aspect of the invention, may be omitted. Each of the several general steps is subject to modification in a number of respects.

In carrying out the first step of the combined to operation of the invention, a stream of oil, originally distilled from the raw charging stock within the operation, is heated to a high cracking temperature in a primary heating operation, the hot oil products of this primary heating opera-- 55 tion together with rawcharging stookwhich, h w.

ever, is not as such subjected to this heating operation, are subjected to a tar separating and evaporating operation, tar including tar constituents of the raw charging stock is discharged from this tar separating and evaporating operation, the vapors escaping from this tar separating and evaporating operation are subjected successively to a primary fractionating operation and a secondary fractionating operation, a higher boiling high boiling condensate including constituents of the raw charging stock subjected to and evaporated in the tar separating and evaporating operation is condensed in the primary fractionating operation and a lower boiling high boiling condensate is condensed in the secondary fractionating operation, the condensate condensed in the primary fractionating operation, but not that condensed in the secondary fractionating operation, is supplied to the primary heating operation, and a gasoline fraction is taken off from the secondary fractionating operation and condensed. The two fractionating operations are controlled to separate in the primary fractionating operation a condensate sufiiciently free from refractory constituents not to impair to any substantial extent the production rate or efiiciency of the primary heating operation and to separate in the secondary fractionating operation a condensate including refractory constituents which, if supplied to the primary heating operation, might accumulate, or tend to accumulate, within the operation. This condensate including the more refractory constituents, or at least a major proportion of the more refractory constituents, is discharged, hot, from the secondary fractionating operation. The raw charging stock may be supplied to the tar separating and evaporating operation in a number of ways. It is advantageously supplied as a sc -called quenching stock to limit further cracking, in the tar separating and evaporating operation, of hot oil products discharged from the primary heating operation.

In carrying out the second step of the combined operation of the invention, the hot condensate discharged from the secondary fractionating operation, in the first step, is separately heated to a higher cracking temperature in a secondary heating operation, the hot oil products of this secondary heating operation are subjected to another tar separating operation from which separated tar is discharged, the vapors escaping from this tar separating operation are separately subjected to another fractionating operation, a high boiling condensate is condensed in this fractionating .op-

eration, and a gasoline fraction is taken off from this fractionating operation and condensed. The high boiling condensate condensed in this fractionating operation is not permitted to return to either the primary heating operation or the secondary heating operation but is discharged, hot, from this fractionating operation. A part of this high boiling condensate, or a part of the tar discharged from the tar separating operation in the second step, or all or a part of the tar discharged from either or both of the tar separating operations in the first and third steps, may be supplied, after cooling, to the tar separating operation, in the second step, as a quenching stock.

In carrying out the third step of the combined operation of the invention, the hot condensate discharged from the fractionating operation in the second step is separately heated to a still higher cracking temperature in a tertiary heat ing operation, the hot oil products of this tertiary heating operation are subjected to still another tar separating operation from which separated tar is discharged, the vapors escaping from this tar separating operation are separately subjected to still another fractionating operation, a high boiling condensate is condensed in this fractionating operation and a gasoline fraction is taken off from this fractionating operation and condensed. The high boiling condensate condensed in this fractionating operation is not permitted to return either to the primary heating operation or to the secondary heating operation but at least a part of this high boiling condensate is discharged from this fractionating operation and this discharged part is'not permitted to return to the tertiary heating operation. A part of this high boiling condensate may be supplied to the tertiary heating operation together with the hot condensate discharged from the fractionating operation in the second step. A part of this high boiling condensate, or a part of the tar discharged from the tar separating operation in the third step, or all or a part of the tar discharged from either or both of the tar separating operations in the first two steps, may be supplied, after cooling, to the tar separating operation, in the third step, as a quenching stock. The tar discharged from the tar separating operation, in the first step and, advantageously, in the third step, is advantageously supplied to a coking operation through which the hot oil products from the tertiary heating operation pass to this tar separating operation. When sufiicient heat is available, as is usually the case when the stock or stock mixture is heated to a cracking temperature in the higher range of cracking temperatures in the tertiary heating operation, tar discharged from the tar separating operation in the second step may also be supplied to such a coking operation. The return of a part of the high boiling condensate condensed in the fractionating operation in the third step to the tertiary heating operation is useful particularly when the combined operation includes such a coking operation; when the combined operation does not include such a coking operation it is usually more advantageous to discharge all of this 'high boiling condensate condensed in the fractionating operation in the third step without permitting any part of it to return to any of the heating operations.

In the primary heating operation the oil may be heated, for example, to a temperature approximating 900-950 F., in the secondary heating operation, for example, to a temperature approximating 925975 F. or 1000ll00 F., and in the tertiary heating operation, for example, to a temperature approximating 935-975 F., or 1050- 1150 F. The cracking operation embodied in the first step of the combined operation of the invention is advantageously of the so-called pressure coil type, that is an operation in which the oil is heated to a cracking temperature under superatmospheric pressure, 400-800 pounds per square inch as discharged from the heating operation for example, followed by separation of the thus heated oil into a vaporized fraction and a residual fraction under a lower pressure, 10-50 pounds per square inch for example. The cracking operations embodied in the second and third steps of the combined operation of the invention may similarly be of pressure coil type. The cracking operation embodied in the third step of the combined operation of the invention, however, is advantageously of the so-called vapor phase type, that is an operation in which the oil supplied to the heating operation is heated to a temperature so high with respect to the pressure prevailing therein, 5-50 pounds per square inch as discharged from the heating operation for exam ple, that the hot oil products of the heating operation are discharged therefrom predominantly in vapor phase. The cracking operations embodied in the first and second steps of the combined operation of the invention may similarly be of vapor phase type. In referring to "a high cracking temperature herein reference is intended to cracking temperatures upwards of about 900 F.

In carrying out the combined operation of the present invention, a clean stock to be supplied to the primary heating operation is produced from a dirty charging stock within the first step, two separate high boiling fractions, higher bo=i1- ing than suitable as products of the operation, one more refractory than the other, and this more efractory fraction including a major portion of the more refractory constituents produced and/ or separated in the first step, are separated from the fraction initially vaporized in the first step,

the less refractory fraction is supplied to the primary heating operation and the more refractory fraction is sup-plied to a separate secondary heating operation in which it is subjected to more severe cracking conditions, the accumulation of refractory constituents within the first step being thus avoided, a high boiling condensate, higher boiling than suitable as the product of the operation, more refractory than the stock supplied to the secondary heating operation, is separated from the fraction initially vaporized in the second w step, and this refractory high boiling fraction is supplied to a separate tertiary heating operation in which it is subjected to still more severe cracking conditions in the third step. In each of the three steps of the combined operation of the in- 1 vention the stock supplied to the heating operation is therein subjected to cracking conditions particularly appropriate to the particular stock. The accumulation of refractory constituents within each step is avoided by the discharge of 1 heating operation in the second step, and so on. -When the combined operation of the invention includes a coking operation, the tar separated and produced in the first step, and the tar produced in the second and third steps, is advantageously reduced to coke in this coking operation by direct heat exchange with the hot oil products discharged from the tertiary heating operation, namely those which are discharged at highest temperature. Additional heat, if required, may advantageously be supplied to such a coking operation by returning through the tertiary heating operation and the coking operation a part of the high boiling stock separated in the third step.

The. invention will be further described in connection with the accompanying drawing which illustrates, diagrammatically and conventionally,

in elevation and partly in section and with parts bro-ken away, one form of apparatus adapted for carrying out the process of the invention.

The apparatus illustrated comprises three heating conduits la, lb and lo arranged in heating furnaces 2a, 2b and 20, three. tar separating towers 3a, 3b and 30, four fractionating towers 4, 5a, 5b and 5c, and two coking receptacles 6a and 6b. Raw oil is supplied, by means of pump 1, to the lower part of the tar separating tower 3a through connection 8 after passing through heat exchangers 4 and 5a. Raw oil, or part of the raw oil, may be supplied to the tar separating tower 3a through connection 30 to flow downwardly through the tower to the lower part. Vapors escaping from the upper part of the tar separating tower 3a enter the lower part of fractionating tower 4 through connection 9 and vapors escaping from the upper part of fractionating tower 4 enter the lower part of fractionating tower 5a through connection l0. Tar separated in the tar separating tower 3a is either discharged through connection H or, by means of pump l2, supplied to the coking receptacles 6a and 6b through connections l3 and I4. Condensate separated in the fractionating tower 4 is supplied, by means of pump l5a, to the heating conduit la in which the primary heating operation is carried out. Condensate separated in the fractionating tower 5a is supplied, by means of pump 115b, to the heating conduit lb in which the secondary heating operation is carried out. The hot oil products discharged from the heating conduit la, in which the stock supplied is heated to a high cracking temperature, are discharged into the lower part of the tar separating tower 3a through connection liia including valve l'la which may be used to maintain a pressure differential between the heater discharge and the tar separating tower. The hot oil products discharged from the heating conduit lb, in which the stock supplied is heated to a higher cracking temperature, are discharged into the lower part of the tar separating tower 3b through connection l6b including valve l'lbwhich may be used to maintain a pressure differential between the heater discharge and the tar separating tower. Tar separated in the tar separating tower 3b is either discharged through connection l8 or, through this connection and connection l9, supplied to the coking receptacles 6a and 61), or supplied, by means of pump 20, through cooler 2! and connection 22 to the lower part of the tar separating tower 3b as a quenching stock. Condensate separated in the fractionating tower 5b is supplied, by means of pump I50, to the heating conduit la in which the tertiary heating operation is carried out. Part of this condensate may be supplied, by means of pump 2!), through the cooler 2| and connection 22 to the lower part of the tar separating tower 3b as a quenching stock. The

' stock supplied to the heating conduit is heated therein to a cracking temperature still higher than that to which the stock supplied to the the tar separating'tower 3c is either discharged through connection 26 or, through connection l4,

supplied, by means of pump 21, to the coking receptacles 6a and lib, or, through connections 28 and 29, supplied through a cooler (not shown) to the lower part of the tar separating tower 30 as a quenching stock. Condensate separated in the fractionatingtower cis at least in part discharged through connection 3|. Fart of this condensate may be supplied, by means of pump l 50, through connection 33, to the heating conduit lo in which the tertiary heating operation is carried out together with condensate from the fractionating tower 5b. Part of the condensate separated in the fractionating tower 50 may be supplied, through connections 32 and 29 and a cooler (not shown), to the lower part of the tar separating tower as a quenching stock.

The vapors remaining uncondensed in the fractionating towers 5a, 5b and 5c are discharged through connections 34a, 34b and 340 to conventional condensing, gas separation and recovery apparatus (not shown). Control of the tar separating towers 3a, 3b and 3c is obtained by the direct introduction of a refluxing medium, a

stock vaporizing substantially completely under 1' the conditions of temperature and pressure prevailing in the tar separating tower, for example, through connections 35a, 35b and 350 or by regulated circulation of an indirect cooling medium through the dephlegmators 3a, 3b and 30' or by these means jointly. A partial control of the operation of the fractionating towers 4 and 5a is obtained by the heat exchange between the vapors leaving these towers and the raw oil supplied to the operation in heat exchangers 4' and 5a, dephlegmators with respect to the fractionating towers 4 and 5a respectively. Final control of the fractionating towers 4 and 5a, and control of the fractionating towers 5b and 5c, is obtained by the direct introduction of a refluxing medium through connections 36, 31a, 31b and 310 or by the regulated circulation of an indirect cooling medium through the dephlegmators 4", 5a", 5b and 50' or by these means jointly.

The coking receptacles 6a and 6b may be two of a group of two, three, four or more coking receptacles. The operation of these coking receptacles may be conducted, for example, as described in my application filed February 19, 1929, Serial Number 341,214. In the coking receptacles 6a and 6b, the tar, or similar stock, supplied through connection I4, is reduced to coke by direct heat exchange with the hot oil products discharged from the heating conduit at lc. When a charge of coke accumulates in one coking receptacle, that coking receptacle is out out of operation and the coking operation is continued in the next coking receptacle of the group while the accumulated charge 01' coke is discharged from the first.

If it is desired that the second heating stage be omitted, the condensate separated in the fractionating tower 5a may be diverted, from pump l5b by regulation of the appropriate valves, directly to the heating conduit lc instead of passing directly to the heater lb as above described. The functions of the heater lb and the associated separating tower 3b and fractionating tower 5?) may be omitted entirely in this method of operation.

The invention will be further illustrated by the following example of an operation embodying the invention as practiced in the apparatus illustrated.

A heavy gas oil fraction is condensed in the tower 4 and a light gas oil fraction in the tower 5a, each of these fractions including constituents of a raw topped crude petroleum supplied through connection 8 to the tower 3a and vaporized therein and constituents of the hot oil products discharged from the heater la separated as vapors in the tower 3a. The heavy gas oil condensed in the tower 4 is heated to a temperature of 925 F. in the heating conduit la under a pressure, as discharged, of 600 pounds per square inch, this pressure being reduced to a pressure of 40 pounds per square inch as the resulting hot oil products are discharged from the heating conduit la into the heating tower 3a. The light gas oil condensed in the tower 5a is heated to a temperature of 935 F. in the heating conduit lb under a pressure, as discharged, of 700 pounds per square inch, this pressure being reduced to a pressure of 40 pounds per square inch as the resulting hot oil products are discharged from the heating conduit lb into the tower 3b. A light gas oil is condensed in the fractionating tower 5b, and this light gas oil is heated to a temperature of 1120 F. in the heating conduit lc' under a pressure, as discharged, of 50 pounds per square inch, this pressure being reduced to a pressure of 40 pounds per square inch, the pressure prevailing in the tower 30, as the resulting hot oil products pass through the coking receptacle 6a or 6b. A temperature approximating 780 F. is maintained in the lower part of the tower 3a and a temperature approximating 760 F. is maintained in the lower part of the towers 3b and 3c. The tar separated in each of the towers 3a, 3b and 3c is supplied to the coking receptacle through which the hot oil products discharged from the heating conduit lc are passing. A light gas oil is condensed in the tower 5c, 40% of it is discharged through connection 3l and 60% of it is supplied to the heating conduit lc together with the light gas oil from the tower 517. A gasoline fraction is taken off from each of the towers 5a, 5b and 5c and condensed.

I claim:

1. In the manufacture of gasoline by cracking high boiling hydrocarbon oils, the improvement which comprises heating a stream of oil to a high cracking temperature in a primary heating operation, subjecting the hot oil products of this primary heating operation and raw oil not subjected to this heating operation together to a tar separating and evaporating operation and discharging tar including constituents of the raw oil therefrom, subjecting the vapors escaping from this separating and evaporating operation successively to a primary fractionating operation and a secondary fractionating operation, condensing a high boiling condensate including constituents of the raw oil subjected to and evaporated in the separating and evaporating operation in the primary fractionating operation and supplying this condensate to the primary heating operation, condensing a lower boiling high boiling condensate in the secondary fractionating operation, separately heating this secondmentioned condensate to a higher cracking temperature in another heating operation and subjecting the hot oil products of this heating operation to a second tar separating operation and discharging tar therefrom, supplying tar from the first-mentioned tar separating operation to a coking operation through which at least a portion of the hot oil products from the second-mentioned heating operation pass, subjecting the vapors escaping from the second tar separating operation to a fractionating operation and condensing a high boiling condensate therein, discharging at least a part of this third-mentioned condensate without permitting return of the discharged part to either heating operation, and condensing a gasoline fraction from the vapors escaping from the said secondary fractionating operation and from the subsequently-mentioned fractionating operation.

2. In the manufacture of gasoline by cracking high boiling hydrocarbon oils, the improvement which comprises heating a stream of oil to a high cracking temperature in a primary heating operation, subjecting the hot oil products of this primary heating operation and raw oil not subjected to this heating operation together to a tar separating and evaporating operation and discharging tar including constituents of the raw oil therefrom, subjecting the vapors escaping from this separating and evaporating operation successively to a primary fractionating operation and a secondary fractionating operation, condensing a high boiling condensate including constituents of the raw oil subjected to and evaporated in the separating and evaporating operation in the primary fractionating operation and supplying this condensate to the primary heating operation, condensing a lower boiling high boiling condensate in the secondary fractionating operation, separately heating this second-mentioned condensate to a higher cracking temperature in a secondary heating operation, subjecting the hot oil products of this secondary heating operation to a second tar separating operation and discharging tar therefrom, separately subjecting the va pors escaping from this separating operation to a fractionating operation and condensing a high boiling condensate therein, separately heating this third-mentioned condensate to a still higher cracking temperature in a tertiary heating operation and subjecting the hot oil products of this tertiary heating operation to a third tar separating operation, supplying tar from the first-mentioned tar separating operation to a coking operation through which at least a portion of the hot oil products from the tertiary heating operation pass, separately subjecting the vapors escaping from the third tar separating operation to a fractionating operation and condensing a high boiling condensate therein, and condensing a gasoline fraction from the vapors escaping from the said secondary fractionating operation and from each of the two subsequently-mentioned fractionating operations.

3. In the manufacture of gasoline by cracking high boiling hydrocarbon oils, the improvement which comprises heating a stream of oil to a high cracking temperature in a primary heating operation, subjecting the hot oil products of this primary heating operation and raw oil not subjected to this heating operation together to I a tar separating and evaporating operation and discharging tar including constituents of the raw oil therefrom, subjecting the vapors escaping from this separating and evaporating operation successively to a primary fractionating operation and a secondary fractionating operation, condensing a high boiling condensate including constituents of the raw oil subjected to and evaporated in the separating and evaporating operation in the primary fractionating operation and supplying this condensate to the primary heating operation, condensing a lower boiling high boiling condensate in the secondary fractionating operation, separately heating this second-mentioned condensateto a higher cracking temperature in another heating operation and subjecting the hot oil products of this heating operation to a tar separating operation and discharging tar therefrom, supplying tar from the first-mentioned and the second-mentioned tar separating operations to a coking operation through which at least a portion of the hot oil products from the second-mentioned heating operation pass, subjecting the vapors escaping from the second-mentioned tar separating operation to a fractionating operation and condensing a high boiling condensate therein, discharging at least a part of this third-mentioned condensate without permitting return of the discharged part to either heating operation, and condensing a gasoline fraction from the vapors escaping from the said secondary fractionating operation and from the subsequently-mentioned fractionating operation.

4. In the manufacture of gasoline by cracking high boiling hydrocarbon oils, the improvement which comprises heating a stream of oil to a high cracking temperature in a primary heating opjected to this heating operation together to a tar separating and evaporating operation and discharging tar including constituents of the raw oil therefrom, subjecting the vapors escaping from this separating and evaporating operation successively to a primary fractionating operation and a secondary fractionating operation, condensing a high boiling condensate including constituents of the raw oil subjected to and evaporated in the separating and evaporating operation in the primary fractionating operation and supplying this condensate to the primary heating operation, condensing a lower boiling high boiling condensate in the secondary fractionating operation, separately heating this secondmentioned condensate to a higher cracking temperature in a secondary heating operation, subjecting the hot oil products of this secondary heating operation to a second tar separating operation and discharging tar therefrom, separately subjecting the vapors escaping from the second tar separating operation to a fractionating operation and condensing a high boiling condensate therein, separately heating this thirdmentioned condensate to a still higher cracking temperature in a tertiary heating operation and subjecting the hot oil products of this tertiary heating operation to a third tar separating operation, supplying tar from the first-mentioned and the second-mentioned tar separating operations to a coking operation through which at least a portion of the hot oil products from the tertiary heating operation pass, separately subjecting the vapors escaping from the third tar separating operation to a fractionating operation and condensing a high boiling condensate therein, and condensing a gasoline fraction from the vapors escaping from the said secondary fractionating operation and from each of the two subsequently-mentioned fractionating operations.

HARRY L. PELZER. 

